refactor: convert repository to monorepo with npm workspaces

Restructured the repository into a monorepo to better organize application code
and maintenance scripts.

## Workspace Structure
- web-app: Next.js application (all app code moved from root)
- housekeeping: Database backup and maintenance scripts

## Key Changes
- Moved all application code to web-app/ using git mv
- Moved database scripts to housekeeping/ workspace
- Updated Dockerfile for monorepo build process
- Updated docker-compose files (volume paths: ./web-app/etc/hosts/)
- Updated .gitignore for workspace-level node_modules
- Updated documentation (README.md, CLAUDE.md, CHANGELOG.md)

## Migration Impact
- Root package.json now manages workspaces
- Build commands delegate to web-app workspace
- All file history preserved via git mv
- Docker build process updated for workspace structure

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

web-app/app/ui/AddLocationButton.tsx

@@ -0,0 +1,30 @@
+"use client";
+
+import { PlusCircleIcon, HomeIcon } from "@heroicons/react/24/outline";
+import { YearMonth } from "../lib/db-types";
+import { formatYearMonth } from "../lib/format";
+import Link from "next/link";
+import { useTranslations } from 'next-intl';
+
+export interface AddLocationButtonProps {
+    /** year and month at which the new billing location should be addes */
+    yearMonth: YearMonth;
+    className?: string;
+}
+
+export const AddLocationButton:React.FC<AddLocationButtonProps> = ({yearMonth, className}) => {
+
+    const t = useTranslations("home-page.add-location-button");
+
+    return(
+        <div className={`card card-compact card-bordered bg-base-100 shadow-s my-1 ${className}`}>
+            <Link href={`/home/location/${ formatYearMonth(yearMonth) }/add`} className="card-body tooltip self-center" data-tip={t("tooltip")} data-umami-event="add-new-location">
+                <span className='flex self-center'>
+                    <HomeIcon className="h-[1em] w-[1em] cursor-pointer text-4xl mt-[.1rem]" />
+                    <PlusCircleIcon className="h-[1em] w-[1em] cursor-pointer text-xl text-green-500 ml-[-.6em] mt-[-.3em]"  />
+                    <span className="ml-1 self-center text-sm sm:text-xs text-left w-[5.5em] leading-[1.3em]">{t("tooltip")}</span>
+                </span>
+            </Link>
+        </div>
+    );
+}